When to plant in Oswego, IL
USDA Zone 5bEverything below — frost dates, hardiness zone, and what to plant when in Oswego, Illinois — is derived from the closest NOAA station with complete climate normals.
In zone 5b, Oswego gardeners can grow many hardy perennials, while the last and first frost still dictate the annual vegetable calendar.
Frost probability
AURORA · 1991–2020The date the last spring and first fall frost occur, by threshold and probability. A 90% date is later in spring — and earlier in fall — than a 10% date; the 50% · 32°F row is what most gardeners plan around. These are Oswego’s own odds, recorded at AURORA.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | May 19 | May 1 | Apr 17 | Sep 29 | Oct 13 | Oct 25 |
| 32°F | May 4 | Apr 19 | Apr 5 | Oct 9 | Oct 23 | Nov 3 |
| 28°F | Apr 23 | Apr 8 | Mar 25 | Oct 21 | Nov 2 | Nov 16 |
Download this table as CSV ↓ — every threshold and probability, plus this city’s planting-window dates.
What to plant now
TODAY · JULY 19Full-year planting calendar
Each bar is the exact window to take a planting action in Oswego, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 23 km · complete 32°F normalsWhen stations disagree by more than a few days, that spread is real microclimate variation — elevation, water, urban heat. Judge which station best matches your own yard.
Oswego planting FAQ
When is the last spring frost in Oswego, IL?
Plan for the last spring frost in Oswego around April 19 (the date it has a 50% chance of a 32°F freeze). Anything frost-sensitive should go out after it.
When is the first fall frost in Oswego, IL?
The first fall frost in Oswego typically arrives around October 23 (50% probability at 32°F). Harvest or protect frost-sensitive crops before then.
What hardiness zone is Oswego in?
Oswego is in USDA hardiness zone 5b. In zone 5b, winters are cold — pick cold-hardy varieties and protect tender crops.
How long is the growing season in Oswego?
Oswego has about 187 frost-free days — a moderate growing season — between the average last spring frost (April 19) and first fall frost (October 23).
When should I plant tomatoes in Oswego?
For Oswego, sow tomatoes indoors about February 22–March 8 and move the seedlings out around April 26, after the last spring frost.
Never miss a window in Oswego
An email when it’s time to start seeds, transplant, and sow — timed to Oswego’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Montgomery · 4 km
- Yorkville · 8 km
- Aurora · 10 km
- Plainfield · 12 km
- North Aurora · 14 km
- Plano · 16 km
- Naperville · 16 km
- Batavia · 18 km
Frost dates recorded at AURORA, 11 km from the city center · 1991–2020 NOAA climate normals · zone from the USDA/PRISM 2023 map. How we compute this.
BlissGarden. "When to Plant in Oswego, IL — Frost Dates & Zone 5b." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00110338. Retrieved from https://blissgarden.com/illinois/oswego.